Ben H. Choi

Do radial glia give rise to both astroglial and oligodendroglial cells

Abstract The development and differentiation of glial cells in the human fetal spinal cord was studied by correlative electron microscopic and immunohistochemical analysis in 20 embryos and fetuses between 6 and 17 weeks of ovulation age. Gliogenesis is characterized initially by the formation of radial glia and astroglia and subsequently, when myelination is about to begin, by the formation of oligodendroglia. The radial glial origin of astroglial cells has previously been demonstrated. The finding of ‘transitional’ cells with cytological, ultrastructural and immunohistochemical features intermediate between those of astroglial and oligodendroglial cells and the close relationship that develops between astroglial cells and axons just prior to the onset of myelination suggest that oligodendroglia may also be derived from radial glial cells, either directly or through intermediate astroglial forms.

Glial fibrillary acidic protein in radial glia of early human fetal cerebrum: a light and electron microscopic immunoperoxidase study

In order to assess the nature of glial fibrillary acidic protein (GFAP) immunoreactivity in the radial glia of early human fetal cerebrum, full thickness blocks from the midconvexity of the frontoparietal region of the cerebrum of 25 human fetuses ranging from ten to 20 weeks of ovulation age were studied by light and electron microscopic (EM) immunoperoxidase methods. The presence of GFAP within radial glia was demonstrated in vibratome sections, in de-eponized 1 μm sections and in paraffin-embedded sections both at light and EM levels in suitably fixed human fetal cerebral tissue. The results indicate that the pattern of GFAP immunoreactivity observed in “routinely” processed autopsy brains, in which fixation is suboptimal, must be interpreted with care.

Altered distribution of excitatory amino acid receptors in temporal lobe epilepsy

In temporal lobe epilepsy, excitatory amino acid receptors in the hippocampus and temporal lobe may contribute to both increased excitability and vulnerability to excitotoxic damage. We used receptor autoradiography to examine the density of N-methyl-D-aspartate (NMDA) and kainic acid (KA) receptors in the hippocampus and parahippocampal gyrus obtained from five patients who had undergone anterior temporal lobectomy for the treatment of intractable seizures and from six control individuals, in which the hippocampus was obtained postmortem. Within the hippocampal formation, loss of [3H]KA and NMDA-sensitive L-[3H]glutamate binding was apparent in the sclerotic regions CA3, hilus, and CA1. In the subiculum and molecular layer of the denate gyrus, binding densities were maintained or even increased in some of the epileptic patients. A two-fold increase in L-[3H]glutamate binding, along with an increase in [3H]KA binding, was observed in the parahippocampal gyrus obtained from the epileptic patients. The results suggest that the vulnerability of the hippocampus in temporal lobe epilepsy may result, at least in part, from the presence of aberrant excitatory circuits in the parahippocampal gyrus.

Physiologic and histologic changes in near-term fetal lambs exposed to asphyxia by partial umbilical cord occlusion

OBJECTIVES Our purpose was to characterize the histologic changes in the asphyxiated fetal lamb brain and to correlate the severity of these changes with fetal physiologic parameters during and after asphyxia. STUDY DESIGN Seventeen near-term fetuses were used for analysis: control group without manipulation (n = 4, 132 +/- 1.1 days of gestation at autopsy, mean +/- SEM), sham-asphyxia control group (n = 3, 132 +/- 1.3 days), and asphyxiated group, which successfully survived 72 hours after asphyxia (n = 10, 130 +/- 1.0 days). Asphyxia was produced by umbilical cord occlusion lasting for approximately 60 minutes until fetal arterial pH diminished to < 6.9 and base excess to < -20 mEq/L. Fetal heart rate, blood pressure, and electrocorticographic activity were continuously monitored. The fetuses were killed 72 hours after asphyxia, and the brains were fixed in formalin and processed for histologic and immunocytochemical studies. RESULTS Neuropathologic changes varied from case to case, ranging from almost total infarction of cortical and subcortical structures to extremely subtle and patchy white matter alterations characterized by slight vacuolization of the white matter or slight to moderate increases in cellularity confined to the junction of cerebral cortex and white matter. Even fetuses that showed full recovery of all physiologic parameters, including electrocorticographic activity, demonstrated subtle but distinct white matter lesions. The gray matter, including the hippocampal neurons, was generally spared in these cases. Electrocorticographic parameters, duration of hypotension during asphyxia, and delayed recovery of blood lactate concentrations correlated well with the histologic grading of brain damage. CONCLUSIONS Asphyxia by partial umbilical cord occlusion in near-term fetal lambs produces variable neuropathologic changes. The mildest change is a white matter lesion characterized by vacuolization and loss of myelin or by increased cellularity in the damaged regions.

Increased expression of the embryonic form of a developmentally regulated mRNA in Alzheimer's disease

There is increasing evidence that an aberrant sprouting response may contribute to some of the neuronal alterations observed in Alzheimers disease (AD). In this study, we demonstrate that in the rat CNS, sprouting results in the reinduction of the embryonic form of the mRNA for alpha-tubulin. The fetal form of alpha-tubulin mRNA was also elevated in the hippocampus obtained from five AD patients, as compared to five elderly controls. These results suggest that the reexpression of embryonic forms of cytoskeletal proteins, in association with an aberrant sprouting response, may contribute to the neuropathological alterations in AD.

Density and distribution of excitatory amino acid receptors in the developing human fetal brain: A quantitative autoradiographic study

The binding of [alpha-3H]amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) to quisqualate receptors, [3H]kainate (KA) to KA receptors, and L-[3H]glutamate to N-methyl-D-aspartate (NMDA) receptors was determined by quantitative autoradiography in brains obtained from twelve aborted human fetuses ranging from 16.5 to 26 weeks of gestational age. Among the three receptor subtypes, specific binding to AMPA was the highest, followed by NMDA and KA, respectively, in all age groups. Receptor binding was already apparent by 16.5 weeks in the hippocampus, thalamus, and subthalamic nucleus, rose sharply by 20-21.5 weeks, and subsequently declined to their lowest levels by 24-26 weeks. Anatomically distinct binding patterns for each of the three major excitatory amino acid (EAA) receptor subtypes were well established by 20-21.5 weeks. Within the hippocampus, AMPA was localized primarily in the stratum pyramidale, NMDA in the stratum radiatum, and KA in the molecular layer of the dentate gyrus and in the stratum lucidum of the CA3 region. The cerebral cortex showed dense labeling of AMPA in the outer layers, whereas KA binding was more prominent within the inner layers. The putamen and globus pallidus also showed relatively dense receptor binding in all age groups. The sharp rise in receptor density at 20-21.5 weeks of age suggests involvement of EAA pathways in developmental plasticity, including reorganization of neuronal processes or synapses, during this period of development. Developmental changes in the density and distribution of EAA receptors, as shown in this study, may also provide insight into shifts in the localization of age-dependent selective vulnerability within the developing human fetal brain.

The ventriculus terminalis and filum terminale of the human spinal cord

Serial sections of the conus medullaris and the filum terminale of 23 randomly selected human spinal cords were studied by light and electron microscopy, and following immunoperoxidase staining for glial fibrillary acidic protein (GFAP), vimentin, neuron-specific enolase (NSE), amyloid beta protein, and S-100 protein. The intradural portion of the filum contains bundles of GFAP-positive glial fibers, scattered silver- and NSE-positive neurons, segments of peripheral nerve, blood vessels, fibrous connective tissue, and fat. Glial cell clusters varying from five to 100 cell layers thick at times constitute the bulk of the filum. The periependymal glial cells possess moderate amounts of eosinophilic cytoplasm and relatively uniform round to ovoid nuclei containing evenly distributed chromatin. They are distributed diffusely with no specific pattern of organization, although some of them showed a tendency to form acinar structures. A minority of the glial cells showed GFAP immunoreactivity, and some were immunoreactive for vimentin. Electron microscopy demonstrated the presence of periependymal cells showing cilia, microvilli, and the formation of intercellular junctional complexes, as well as cells containing bundles of glial filaments within the cytoplasm. Degenerated NSE-positive neurons and degenerated neurites resembling neuritic plaques were also demonstrated. However, immunoperoxidase staining for amyloid beta protein was negative in these structures. Thus, the filum terminale is endowed with an abundance of glial cells and neurons and is not simply a fibrovascular tag. Periependymal glial cells in the filum terminale should not be mistaken for neoplasm. The presence of neuropil with profuse astroglial and neuronal components within the filum terminale suggests a possible functional role for these structures.

Oxidative stress, brain white matter damage andintrauterine asphyxia in fetal lambs

In order to examine the role of oxidative stress in asphyxia‐induced perinatal braindamage, near‐term fetal lambs were subjected to umbilical cord occlusion for approximately 60 min until fetal arterial pH diminished to less than 6.9 and base excess to less than −20 meq/l. Thelevels of superoxide, hydrogen peroxide, glutathione (GSH) and thiobarbiturate‐reactivesubstances (TBARS) within brain grey and white matter were determined at 72 h to correlatewith morphological changes. Although the topography and extent of brain damage variedsomewhat from case to case, ranging from focal infarction in grey or white matter to subtle andpatchy alterations of white matter, the telencephalic white matter appeared to bear the brunt ofdamage as compared to other regions. The parietal white matter, in particular was often the seatof early pathological changes that could be seen in isolation. These white matter changes wereaccompanied by significant increases in hydrogen peroxide and TBARS levels as compared tothose in grey matter. In another set of experiments, 8 different brain regions were assayed forTBARS, GSH and superoxide dismutase (SOD). A highly significant rise in the levels of TBARSwas again noted in the parietal and frontal white matter. SOD levels were higher in the frontal andparietal white matter, basal ganglia and cerebellum. Cerebral cortical and hippocampal neuronswere relatively unaffected until accompanied by more severe damage to grey and white matter atother sites. These results suggest that the developing telencephalic white matter appears to bemost vulnerable to the effects of intrauterine fetal asphyxia and that oxidative stress may be amajor contributing factor in the pathogenesis of perinatal hypoxic–ischemic encephalopathy.

Cytotoxic effects of repin, a principal sesquiterpene lactone of Russian knapweed.

Repin is the principal sesquiterpene lactone isolated from Russian knapweed (Centaurea repens), a perennial weed found in many parts of the United States. Ingestion of Centaurea repens by horses has been reported to cause a movement disorder simulating Parkinsons disease (PD) and nigrostriatal degeneration, called equine nigrostriatal encephalomalacia (ENE). To understand the mechanisms whereby ingestion of Centaurea repens induces ENE and a PD‐like disorder, repin cytotoxicity was examined to explore its pathogenetic relationship to ENE and to PD. Repin was highly cytotoxic to both PC12 cells and mouse astrocytes in a dose‐ and time‐dependent manner. The cytotoxic effects were accompanied by depletion of glutathione (GSH), a rise in the level of reactive oxygen species (ROS) and damage to cellular membranes. Although repin is a highly reactive electrophile that can readily conjugate GSH, GSH depletion may not be the sole mechanism underlying repin cytotoxicity as shown by our study using buthionine sulfoximine, in which severe GSH depletion did not result in a parallel increase in cell death. However, pre‐treatment with GSH‐glycoside or with lipoic acid provided significant protection from repin‐induced cell death. These data suggest that oxidative stress plays a major role in repin cytotoxicity. Since oxidative stress is considered to play a major role in neuronal degeneration accompanied by depletion of mitochondrial GSH and an increase in lipid peroxides in the substantia nigra of PD, further elucidation of mechanisms of repin neurotoxicity may generate clues regarding not only the mechanisms of neuronal degeneration but also the possible role of environmental factors in the pathogenesis of PD. J. Neurosci. Res. 47:90–97, 1997.

Hemodynamic and electrophysiological effects of mercury in intact anesthetized rabbits and in isolated perfused hearts

Using intact anesthetized rabbits and isolated perfused hearts, the hemodynamic and electrophysiological effects of mercury (Hg) were examined in order to assess the role of cardiovascular dysfunction in Hg intoxication. The most consistent and prominent cardiovascular effect was a significant reduction in blood pressure. This cardiodepressive action was probably brought about by the primary action of Hg on the heart rather than by altered sympathetic activity, as evidenced by normal renal nerve activity at times when the hemodynamic actions of Hg were clearly manifest. Although the principal target organ for the toxic actions of inorganic Hg is the kidney, chronic exposure to both inorganic and organic Hg frequently results in signs and symptoms of CNS dysfunction. The profound hemodynamic effects of Hg that we have observed emphasize the potential importance of Hg cardiotoxicity and indicate the need to differentiate between the primary and the secondary effects of Hg intoxication on CNS tissues for evaluation of the toxic effects of Hg compounds.